1. Technical Field
The present invention relates to light-emitting diode (LED) packaging structures of low angular correlated color temperature deviation, and more particularly, to a light-emitting diode (LED) packaging structure of low angular correlated color temperature deviation, wherein the LED packaging structure is capable of mixing light uniformly.
2. Description of Related Art
Due to technological advancement, white LED manufacturing methods abound. For example, white light is produced by mixing light with a red LED chip, a green LED chip, and a blue LED chip or by exciting red phosphor materials, green phosphor materials, and blue phosphor materials with an ultraviolet LED chip. At present, the commonest white LED packaging method involves covering the blue LED chip with a phosphor body that contains yellow phosphor materials and exciting yellow phosphor materials with blue light so as to produce white light. Although the aforesaid method is flawed with low optical performance of the white light produced, it is advantageously effective in cutting white LED manufacturing costs.
Referring to FIG. 1, there is shown a cross-sectional view of a conventional LED packaging structure 100 with a reflector 500. The conventional LED packaging structure 100 with the reflector 500 comprises a blue LED chip 200 disposed in the reflector 500. The reflector 500 is coated with and filled with a phosphor body 300 that contains yellow phosphor materials for enclosing the blue LED chip 200. However, since the blue LED chip 200 emits light in a Lambertian emission pattern, not only does it manifest maximum light energy at the zero-angle light in a normal direction, but the light energy decreases as the angle increases, wherein the zero-angle light in the normal direction is the light which is perpendicular to an upper surface of blue LED chip 200. Hence, from the perspective of an angular field, horizontally oriented white light is more likely to be confronted with blue light insufficiency than zero-angle white light in the normal direction is. The light intensity of the zero-degree light in the normal direction emitted from the blue LED chip 200 is higher than the light intensity of light emitted in other directions, and thus zero-angle white light in the normal direction is characterized by surplus blue light.
Referring to FIG. 2, there is shown a graph of correlated color temperature against view angle. From the perspective of the graph of correlated color temperature (CCT) against view angle, since the light intensity of the blue LED chip 200 varies with a view angle, not only does the curvature of the curve in the graph vary greatly with the view angle, but CCT in horizontal orientation is increasingly lower than that in normal direction, wherein the conventional LED packaging structure 100 with the reflector 500 has angular correlated color temperature deviation (ACCTD) of 1500˜3000K approximately.
With the conventional LED packaging structure 100 with the reflector 500 having extremely high ACCTD and thus large spatial CCT deviation, the light emitted from the conventional LED packaging structure 100 with the reflector 500 for use with a lamp manifests an apparent yellow halo and a lack of uniformity in light mixing.
Referring to FIG. 3, there is shown a cross-sectional view of a conventional hemisphere LED packaging structure. To solve the aforesaid problem pertaining to overly high ACCTD, the industrial sector developed a hemispherical LED packaging structure 101. The hemispherical LED packaging structure 101 comprises the phosphor body 300 which contains yellow phosphor materials and is shaped like a hemisphere for enclosing the blue LED chip 200. A transparent lens 400 with a hemispherical shape covers the phosphor body 300. The hemispherical LED packaging structure 101 reduces ACCTD to 500˜750K approximately, thereby easing the problem of overly high ACCTD slightly and enhancing uniformity in light mixing. Still, an LED packaging structure that ensures high uniformity in light mixing at every angle remains unavailable. Accordingly, it is imperative to reduce the angular correlated color temperature deviation further and efficiently.